1. Field of the Invention
This invention relates to photosensitive devices of the so-called "line transfer" type for scanning light images.
2. Description of the Prior Art
As described in U.S. patent application Ser. No. 368,005, now U.S. Pat. No. 4,506,246, and Ser. No. 562,462, now U.S. Pat. No. 4,611,234, assigned to THOMSON-CSF, this type of device mainly comprises:
a photosensitive region consisting of M lines each made up of N photosensitive points, the image to be read being projected onto said region and converted to electric charges designated as signal charges; PA0 an interface element consisting of M points, or so-called line memory, which is connected by means of conductive columns to the photosensitive points of the different lines and is intended to receive successively the signal charges stored by each line; PA0 a shift register of the type known as a charge-coupled device (CCD) for receiving the contents of the line memory in parallel and delivering the image-scan electric signal in series.
Preferably, the photosensitive device described above comprises means for removing parasitic charges and said means can be associated with the line memory as described in the patent applications cited earlier.
In order to increase the speed of transfer of the signal charges as well as the efficiency of transfer, the read register usually consists of a CCD register of the volume or bulk transfer type. Such a CCD register is also known as the buried channel type to differentiate it from the surface channel type.
However, when it is desired, for example, to inject charges from the read register to the line memory as described in U.S. patent application Ser. No. 562,462, now U.S. Pat. No. 4,611,234, it is no longer possible to employ a volume transfer into the read register. In this case, in respect of one and the same voltage applied to the gates, the surface potentials are at a higher level than in the case of a surface transfer and the charges present within the shift register cannot pass into the line memory.